1. Field of the Invention
The invention relates to rails such as a monorail track and, more particularly, relates to a rail section having a vertical bend to effect an elevation change along the length of the rail section. The invention additionally relates to a method of bending a rail section about its major axis to produce an elevation change in the rail section.
2. Discussion of the Related Art
It is often desirable in article or personnel conveyance applications to effect a change in elevation along the length of a section of a rail. For instance, in a monorail track used, e.g., to support article transportation devices such as a wheeled carrier cell usable in a sortation system, it may be necessary to effect an elevation change within a rail section to permit the article transportation device to move from one operating level to another. It may also be necessary to employ a non-horizontal rail section to accommodate unintended vertical misalignment between track sections. However, it is difficult to bend practically any rail structure so as to effect an elevation change because the rail must be bent along its major axis--a very difficult task. For instance, a monorail track of the type used to support carrier cells or the like is composed of a plurality of interconnected rail sections. Each rail section generally has an I-beam construction including an upper flange or rail and a lower flange or rail connected to one another at their transverse centers by a vertically oriented web which extends colinearly with the major longitudinal axis of the rail. Each rail section is usually formed integrally from a single metal element such as extruded aluminum. Bending a rail section of this configuration (or virtually any other standard configuration) vertically so as to effect an elevation change along the length of the rail section is extremely difficult, particularly in the field where access to special bending tools is limited at best. This is because the entire cross-section of the rail section must be deformed at the location of the bend with one of the flanges being stretched and the other one being compressed. Bending necessarily surpasses the rail section's yield point, resulting in plastic deformation, so that the rail section retains the intended deformation. However, introducing plastic deformation into the rail section effectively renders it impossible to return the rail section to its original, linear configuration. Therefore, a rail section that is bent for a particular purpose usually cannot be bent into a different shape and used for another purpose.
The difficulties associated with bending rail sections have required the exploration of other options to effect vertical change along the length of the rail section. For instance, height changes are effected in extruded aluminum monorail track structures by forming a multi-piece monorail track section by cutting a curved web out of a sheet of track material and by attaching to this curved web pre-bent top and bottom sections having the desired curvature. The resulting three-piece vertical curve assembly effects the desired inclination change but requires the performance of a relatively difficult, time consuming, and expensive process that generally cannot be performed in the field. Hence, the conventional monorail track structure must be laid out very precisely in advance so that elevation changes within the track may be effected via use of vertically curved track sections that are prefabricated to provide a specific elevation or inclination change. This design requirement places considerable limits on the versatility of track design and makes it nearly impossible to effect a "field fix" to accommodate for unanticipated elevation changes in the track layout.